Various devices are known in the art that use the action of radio-wave interferometer with the use of a compensation channel for separating the modulated component of a radio-frequency signal, which corresponds to the pulse or breath rate of a human being (RU, A, 2159942).
A microwave locator is known that comprises a modulator and a transmitter consisting of a generator, a power divider, a transmitting antenna, which are connected by their signal inputs to their signal outputs in series, and a receiver made with the possibility of emitting a radio-frequency modulated signal, which consists of a receiving antenna, a VHF receiver, a preamplifier/demodulator, a signal processing unit, which are connected by their signal outputs to their signal inputs in series, and made with the possibility of receiving a reflected radio-frequency signal modulated by the pulse and/or breath component from a living being and separating this component at the output of the preamplifier/demodulator, wherein the second signal output of the power divider is connected to the control input of the VHF receiver, the first control output of the modulator is connected to a transmitter and the second and the third outputs of the modulator are connected to the first and the second control inputs of the preamplifier/demodulator. (U.S. Pat. No. 4,958,638).
A disadvantage of the above technical solutions is their poor interference protection relating to various destabilizing factors influencing the locator operation, such as temperature, instability of locator position due to operator hands motion or trembling, instability of the position (movement) of a living being.
Equipment using ultra-wideband (UWB) signals started becoming common in 1960s after Tektronics and Hewlett-Packard issued stroboscopic oscilloscopes for measuring signal parameters. Stroboscopic oscilloscopes used the property of probing signal regular repetition for series restoration of its form. In combination with a source of an ultra-wideband signal (usually change of voltage with the front of picosecond duration was used) the stroboscopic oscilloscope was named a time-domain reflectometer.
The time-domain reflectometry method (TDR) become widespread not only for studying wave impedance, irregularities of distributed paths, but also for assessing dielectrics properties, determining soil humidity, measurements in semiconductor devices. This method gradually transformed into a wider line of time-domain measurements, where frequency characteristics of objects were obtained through the use of signal digital processing algorithms, e.g., fast Fourier transformation (FFT), which were similar to those measured by circuit frequency analyzers.
Ultra-wideband (UWB) signals are understood as signals for which a proportional frequency band Δf=2(FH−FL)/(FH+FL), where FH is the upper frequency in the signal spectrum, and FL is a low frequency in the area more than 0.25. This definition is not a single one; in some works the term “ultra-wideband signal” provides for a definite physical bandwidth (as a rule not less than 500 MHz), in other cases it is considered that such a bandwidth is located near zero frequency. Therefore such definitions are mostly conditional. But recently this term is of wide use, since radiotechnical processing methods for UWB signals have certain commonality and have been significantly developed. The term is applicable to various systems using electromagnetic signals of nanosecond and picosecond duration, systems of time-domain communication and measurements, time-domain reflectometers, radars with radio pulses with duration of several nanoseconds and less.
Works on creation of nanosecond pulse devices have been described in books, e.g., L. A. Morugin, G. V. Glebovich “Nanosecond Pulse Equipment”, Sov. Radio, 1964; and Yu. A. Ryabinin “Stroboscopic Oscillography”, M., Sov. Radio, 1973. A review of works on findings in the application of picosecond equipment may be found in the book by G. V. Glebovich, A. V. Andriyanov et al. “Object Studies with the Use of Picosecond Pulses”.
Radio I Svyaz, 1984.
The use of UWB signals in the field of location has the same limitations as in VHF locators. Such limitations mainly relate to slow temperature drifts of signal time positions and to short-time changes in the position of a locator or an object under probing. But when using radio signals for stabilizing their time position (phase and frequency) phase locking is widely used, which is very difficult for use in the field of UWB signals when working with pulses of small duration. Nevertheless, stabilization of UWB signal positions is necessary and very important, since a delay of a signal received from a probed object varies with changes in temperature or the locator position. In order to read a signal from a given distance long-term stability of the UWB signal time positions is necessary. But in any electronic circuits the life period of any carriers depends on temperature, and time delay of signals may vary by a value up to 200-500 picoseconds. When using a probing signal with duration less than 1 nanosecond, this does not lead to a change in a delay of received signal amplitude from its maximum to zero value.
Until now no methods of stabilizing time positions of UWB signals are known.
The closest technical solution for the claimed one is an ultra-wideband radar for monitoring people, a patent for which has been granted to McEwan (U.S. Pat. No. 5,361,070).
This radar comprises a driving generator, a randomizer, units of reference delay and adjustable delay, two antennas, a generator of ultra-wideband (UWB) signals, a detector of received signals. For finding and monitoring people the transmitting antenna emits a UWB pulsed signal, and the receiving antenna receives a signal reflected from a human being. A reference delay and an adjustable delay serve only for separating a certain area according to a distance at which a reflected signal is registered.
This known technical solution has limited possibilities of monitoring living people due to the fact that the radar does not provide for searching for people at any distance, and when measuring parameters of a reflected signal the device is subject to influence of destabilizing factors, such as temperature and instability of the positions of both an identified object and the radar itself. When the said factors change, delays of registered signals and, consequently, amplitudes of registered voltages are varied accordingly. Due to the said factors the known radar may serve only as a locator of living beings at a predetermined distance.